The present invention relates to a device for limiting overspeed in a turbomachine such as an aircraft jet engine, in order to guard against turbine shaft breakage, a phenomenon which is extremely rare but the consequences of which may prove disastrous.
When this shaft breaks, the turbine rotor finds itself uncoupled from the fan which was limiting its rotational speed, but the blades of the turbine continue to be turned by the gases leaving the turbomachine combustion chamber. The turbine then begins to “overspeed” or “spin”, thus subjecting the rotor to excessive centrifugal forces liable to cause it to explode, with the risks of puncturing the outer casing of the turbine and also the fuselage of the aircraft equipped with this turbomachine. The overspeed limit is therefore a constraint that absolutely must be observed in turbomachines.